1. Field of the Invention
The present invention relates generally to a mobile communication amplification system applied to a mobile communication system, and more particularly to an apparatus and a method for high efficiency power amplification for efficiently amplifying signals having a large Peak-to-Average Power Ratio (PAPR) in a mobile communication system.
2. Description of the Related Art
Commonly, a power amplifier is classified according to the quantity of operation time and bias current of an output apparatus. Accordingly, a power amplifier may be classified into a class-A amplifier, a class-B amplifier, a class-C amplifier, a class-AB amplifier, a class-F amplifier, a class-S amplifier, etc. Hereinafter, a class-S amplifier and a class-S system using the class-S amplifier will be described and a description for other power amplifiers will be omitted.
FIG. 1 is a block diagram illustrating a conventional class-S system including a class-S power amplifier. Referring to FIG. 1, the class-S system includes a Delta-Sigma Modulator (DSM) 101, a class-S amplifier 107 having a power amplifier 103 and a Band-Pass Filter (BPF) 105, and a linearizer 109. The DSM 101 receives Radio Frequency (RF) signals, converts the RF signals to RF pulse signals through a delta-sigma modulation, and outputs the RF pulse signals to the power amplifier 103. The power amplifier 103 operating in a switching mode amplifies the RF pulse signals input from the DSM 101 according to request levels by a system setup, and outputs the amplified RF pulse signals to the BPF 105. The BPF 105 receives the amplified RF pulse signals and removes switching harmonic from the received signals, thereby restoring the original signals for output. Because the power amplifier 103 operates in a switching mode, it theoretically has an efficiency of 100%.
The linearizer 109 removes non-linear components generated by the DSM 101 and the power amplifier 103 for output.
In order to generate RF pulse signals, the prior art uses an oversampling analog-to-digital converter such as a bandpass DSM. In a conventional mobile communication system, RF signals have a frequency of more than 800 MHz. Accordingly, the prior art is problematic in that it requires a bandpass DSM of oversampling of four times as many as 800 MHz, i.e., oversampling of about 3.2 GHz. For example, an IMT-2000 communication system requires a high speed DSM of more than about 8 GHz.
Additionally, the switching mode power amplifier is problematic in that it must operate at a frequency corresponding to up to minimum five times the input RF frequency, i.e., it must have broadband characteristics, in order to exactly amplify the RF pulse signals output from the DSM. For example, an IMT-2000 communication system requires a switching mode power amplifier operating at about 10 GHz.
However, it is very difficult to actually realize the high speed bandpass DSM and the switching mode power amplifier, and they are very expensive. Further, it is very difficult to match broadband input signals with input impedance of the power amplifier.
A conventional DSM basically uses an oversampling and noise shaping technique in order to increase a Signal-to-Noise Ratio (SNR), and oversampling of four times faster than the sampling speed having a minimum Nyquist sampling rate is required. However, such oversampling has been currently used only in a relatively low frequency application such as an audio system due to limitation of digital technology as described above. Accordingly, it is necessary to provide an apparatus and a method capable of applying the DSM to a mobile communication amplification system.